The long term goal of this proposal is to understand the pathogenesis of necrotizing enterocolitis (NEC) and devise novel therapeutic strategies. NEC is the most frequent and lethal gastrointestinal disorder affecting the intestine of the stressed, preterm infant. NEC reflects a breakdown of the intestinal barrier, which results in translocation of pathogenic bacteria into the circulation, activation of the immune system and initiation of a septic inflammatory response. Maintenance of the intestinal barrier, and therefore protection from NEC, normally occurs through intestinal restitution, in which enterocytes migrate towards the damaged mucosa and re-constitute an intact monolayer. We determined that in vivo enterocyte migration is significantly reduced in the small intestine from neonatal rats with NEC compared with non-NEC rats. This implies that impaired intestinal restitution is pathogenic in the development of NEC. To understand enterocyte migration, we first examined phagocytosis by macrophages, which shares similar morphologic features. We determined that phagocytosis requires Rho-GTPase mediated cytoskeletal rearrangements, and SNARE/coatomer protein mediated membrane delivery. Based on our preliminary data, we hypothesize that impaired restitution in NEC is due to impaired enterocyte migration, and that this is due to defects in cytoskeletal rearrangements and/or membrane trafficking. In order to test this hypothesis, we propose the following specific aims: 1): To determine the role of the cytoskeleton in intestinal restitution by enterocyte migration in vitro. 2): To determine the role of membrane traffic in intestinal restitution by enterocyte migration in vitro. 3): To determine the effect of modulating expression of Rho and SNAREs on enterocyte migration, restitution and resolution of experimental NEC in neonatal rats.